1. Field of the Art
This invention relates to an endoscope for medical use, incorporating an objective lens drive mechanism in association with an optical objective lens system on its insertion instrument, and more particularly to an endoscope with an objective lens drive mechanism permitting to shift the position of at least one lens element of an optical objective lens system in the direction of its optical axis by remote control to vary at least observation depth, image magnification scale or view field angle.
2. Prior Art
In general, endoscopes which are used for medical purposes are largely constituted by a manipulating head assembly to be gripped by an operator to control the operation of the endoscope, an insertion instrument extended out on the front side of the manipulating head assembly for insertion into a body cavity, and a universal cable led out from the manipulating head assembly for connection to a light source. In terms of construction and function, the insertion instrument is composed of a rigid tip end section, an angle section and a flexible rod section, from its fore distal end to proximal end. The flexible rod section, which occupies a major portion of the entire length of the insertion instrument, is arranged to be flexible in arbitrary directions along a path of insertion which may contain bends. The rigid tip end section is provided with at least an illumination window and an observation window, along with an outlet opening of a biopsy instrument channel which is usually provided in the insertion instrument for the purpose of insertion of forceps or other instruments. The angle section is flexible by remote control from the side of the manipulating head assembly. Accordingly, the rigid tip end section can be turned into an arbitrary direction by bending the angle section by remote control.
A light emitting end of a light guide, which consists of a bundle of fiber optics, is disposed in the illumination window on the rigid tip end section of the insertion instrument. The light guide is passed through the insertion instrument and assembled into the universal cable which is led out from the manipulating head assembly as mentioned above. Further, an objective lens system is mounted on an image pickup assembly block within the rigid tip end section of the insertion instrument, along with a solid-state image sensor device which is located at the focus of the objective lens system. Normally, the image pickup assembly block is located substantially at a central position in a cross-sectional area of the rigid tip end section. On the other hand, it is usually the case that an illumination window is provided at one or a plural number of positions in the vicinity of an observation window at the distal end of the image pickup assembly block. Accordingly, the center of observation view field is located substantially at a central position of the insertion instrument, and the illumination window or windows are arranged to irradiate the entire view field including center portions thereof.
The optical objective lens system of the endoscopic image pickup is normally constituted by an objective lens group which is composed of a plural number of lens elements. Preferably, the objective lens group should be able to vary at least the depth of focus, image magnification rate or view field angle depending upon the location of an observation site or the purpose of examination. In this regard, it has thus far been known in the art to arrange one or a plural number of lens elements of an objective lens group to be movable in the direction of optical axis of the objective lens system. For this purpose, an objective lens group is usually mounted on a lens frame which is constituted by a fixed lens frame and a movable lens frame. The movable lens frame is slidably fitted in the fixed lens frame which functions as a guide when the movable lens frame is moved in the direction of optical axis.
Accordingly, the optical objective lens system necessarily includes a drive means for moving the movable lens frame in the direction of optical axis. As for drive means of this sort, for example, there have been proposed a diversity of drives using piezoelectric elements, shape memory alloys, artificial muscle and the like. However, normally a proximal end of a control cable which is connected to a movable lens frame is extended into the manipulating head assembly of the endoscope thereby permitting to shift the position of a movable lens or lenses in the direction of the optical axis by remote control. The movable lens is moved between a fore position closer to the subject side and a rear position closer to the imaging side. Location of the movable lens in the rear position gives a smaller image magnification rate and a greater focal depth. On the other hand, location of the movable lens in the fore position gives a greater image magnification rate and a smaller focal depth. Accordingly, in this case, the operator can shift the position of the movable lens by driving same through the control cable or other suitable transmission member, depending upon the location of an intracavitary portion under examination or the nature of examination. This shift of the movable lens position is feasible even when the insertion instrument of the endoscope is inserted in a body cavity of a patient.
In order to pick up clear images through an optical objective lens system, a movable lens has to be located precisely in either one of the above-mentioned fore and rear positions. This is so especially when a movable lens is located in a fore position on the side of a subject because the focal depth is shallow in the fore position and therefore a slight deviation from a predetermined position will invite considerable deteriorations in quality of picture images. It follows that a movable lens should be positioned correctly at least when shifted to a fore position on the side of a subject. For remote-controlling a movable lens, a control cable is connected to a movable lens frame as mentioned above. Various forms of remote control cables of this sort have been known in the art, for example, from Japanese Laid-Open Patent Specification H4-13112 and Japanese Utility Model Publication S55-55041.
Disclosed in Japanese Laid-Open Patent Specification H4-13112 is a lens group consisting of a front group lens, a rear group lens and a magnification control lens which is movable in the direction of optical axis. The magnification control lens is arranged to slide along a slide member which is provided between front and rear lens frame which support the front and rear lens groups, respectively. The magnification control lens itself is fitted in a magnification lens frame, and an operating wire is connected to the magnification lens frame thereby to permit to move the latter back and forth by remote control from the manipulating head assembly. The operating wire is passed through and fixedly connected at its fore end to a wire threading member which is provided integrally with the rear group lens frame. The other end of the operating wire is connected to a solenoid which is energizable to shift the magnification control lens between a fore position on the side of the front group lens and a rear position on the side of the rear group lens. The control cable of this sort can be referred to as a push-pull type.
Disclosed in Japanese Utility Model Publication S55-55041 is an endoscope employing an image guide in such a way as to vary the distance between a light incident or input end of the light guide and an optical objective lens system. In this particular prior art, the image guide is moved by the use of a control cable. More particularly, in this case, a projection is provided on a mouth piece which is fitted around a fore end portion of an image guide, and a screw shaft threaded into the projection to connect thereto one end of a wire which is passed through a coil tube. In this case, the position of the light input end of the image guide is adjusted by rotating the wire about the longitudinal axis within the coil tube. The control cable of this sort can be referred to as a rotating type.
Of the above-mentioned two types of control cables, the push-pull type can produce a sufficient driving force through the operating wire when the wire is pulled but not when the wire is pushed. Therefore, it becomes necessary to provide a biasing means at the fore end of the operating wire for biasing the multiplication control lens toward the front group lens. The control cable of this type has another problem that, after repeated operations, the operating wire can get elongated to cause variations in pulling stroke length. On the other hand, the rotating type control cable also has inherent drawbacks that its wire easily gets twisted and fails to transmit rotation smoothly to its fore end, and, gets elongated after repeated use similarly to the above-mentioned push-pull type.
In view of the foregoing situations, it is an object of the present invention to provide an endoscope with an objective lens drive mechanism which makes it possible to vary at least the depth of observation, image magnification rate or view field angle of an optical objective lens system.
It is another object of the present invention to provide an endoscope with an objective lens drive mechanism which can transmit driving force securely to a movable lens of an objective lens system in reciprocating the movable lens accurately between predetermined positions and which can be operated constantly in stable conditions.
It is still another and more particular object of the present invention to provide an endoscope with an objective lens drive mechanism which can drive a movable lens of an objective lens system accurately relative to a fixed lens of an objective in alignment with optical axis at least to and from a fore position on the side of a subject and a rear position on the side of an imaging plane.
According to the present invention, in order to achieve the above-stated objectives, there is provided an endoscope with an objective lens drive mechanism which comprises: an optical objective lens system incorporated into a rigid tip end section of an insertion instrument of the endoscope and having a fixed lens mounted on a fixed lens frame provided within the rigid tip end section and a movable lens mounted on a movable lens frame for sliding movement in a direction toward and away from the fixed lens along inner surfaces of the fixed lens frame; guide surfaces formed on inner periphery of said fixed lens frame for guiding sliding movements of the movable lens frame in alignment with optical axis of the objective lens system; a nut portion extended out from the movable lens frame in a radially outward direction substantially perpendicularly to said optical axis of said object lens system; a screw rod extended parallel with the optical axis and held in threaded engagement with the nut portion; a bearing member provided on the fixed lens frame and adapted to support the screw rod rotatably relative to the fixed lens frame but to block movements of the screw rod in an axial direction; and a control cable including a flexible transmission shaft connected between the screw rod and a rotational drive means to transmit rotation from the rotational drive means to the screw rod, and sheathed in a fixed sleeve having a fore end thereof securely fixed to the bearing member.
Regarding the arrangements of the objective lens system and movable lens drive means, in one preferred form of the present invention, a prism securely bonded to the fixed lens frame thereby to turn a light path through 90 degrees toward a light receiving surface of a solid-state image sensor device which is located at the focus of the optical objective lens system substantially in parallel relation with a direction in which the control cable is extended. Regarding the location of the solid-state image sensor device, it is preferable to locate the solid-state image sensor device to a radially opposite side of the optical objective lens system within the rigid tip end section away from the direction of radial extension of the nut portion from the movable lens frame. Alternatively, the solid-state image sensor device may be located in a position intermediate between the movable lens frame and the nut portion.
The movable lens should be located accurately in a predetermined position at least on the side of the subject. For this purpose, preferably the screw rod is provided with a stopper mechanism in associated with the nut portion of said movable lens frame, thereby to stop the movable lens frame at least at a preadjusted stroke end position on the side of the subject. In a more particular form of the present invention, the screw rod is provided with a second screw portion in a fore end portion thereof, and the stopper mechanism is provided with a stopper ring in threaded engagement with the second screw portion of the screw rod in such a way that the position of the stopper ring on the second screw portion can be adjusted to preset the nut portion exactly in a stroke end position of the movable lens on the side of a subject. Preferably, the stopper ring and the nut portion are provided with axially projecting sectoral land portions opposingly on confronting end faces, such that the opposing sectoral land portions are brought into abutting engagement with each other at a predetermined stroke end position of the movable lens. Preferably, the stopper mechanism on the screw rod is arranged to stop the movable lens in both a front stroke end position on the side of a subject and a rear stroke end position on the imaging side of the objective lens system.
In order to let the movable lens frame move smoothly when driven through the control cable, preferably the movable lens frame is provided with a sliding surface at two different positions on the circumference thereof, for sliding contact with inner surfaces of the fixed lens frame. Besides, to lessen frictions between the sleeve and the flexible transmission shaft of the control cable, it is preferred to employ for the sleeve a tube which is treated with a lubricant, for example, a silicon rubber tube which is impregnated with silicon oil.
The nut portion is provided at an outer distal end of an arm portion which is connected to and extended out from the movable lens frame, and has a thickness which is substantially same as axial length of the movable lens frame. Preferably, the arm portion is fitted in and extended through an axial slot which is provided in the fixed lens frame, and thereby blocked against rotational movements relative to the fixed lens frame to preclude the possibilities of positional deviations of the movable lens relative to the fixed lens in the rotational direction. In this connection, the nut portion is preferably provided with an axial extension toward a proximal side of the arm portion thereby to increase a length of threaded engagement with said screw rod. In this case, the bearing member on the side of the fixed lens frame is provided with an open receptacle portion of a diameter larger than outside diameter of the nut portion to receive the axial extension of said nut portion therein.
Further, in a preferred form of the present invention, the rigid tip end section of the insertion instrument is connected to a fore end of an angle section of the endoscopic insertion instrument and has an illumination means and a biopsy instrument channel incorporated thereinto in addition to the optical objective lens system, and a pair of operating wires, more preferably, two pairs of operating wires are connected to the angle section for bending same vertically in upward and downward directions and laterally in rightward and leftward directions. In case the fixed lens frame of the optical objective lens system is located substantially at the center of the rigid tip end section of the endoscopic insertion instrument, it is preferred to connect the movable lens frame and the nut portion by way of an arm portion, and to locate the arm portion in an offset position within the rigid tip end section, shifted by a predetermined angle to the right or left of a center line of upward and downward being motions of the angle section, and to locate the control cable and the biopsy instrument channel on the opposite sides of the center line of bending motions of the angle section. The arrangement makes it possible to bend the angle section smoothly in a reliable manner. Further, in a sectional area of the angle section taken perpendicularly to a longitudinal axis thereof and divided into four subdivisions by two perpendicularly intersecting lines drawn between said first and second pairs of operating wires, it is preferred to locate at least the biopsy instrument channel solely in one of the subdivisions, the control cable in another subdivision along with other internally threaded component parts of the insertion instrument in such a way as to keep balance with the biopsy instrument channel in stiffness in bending directions, and other internally threaded components of the insertion instrument in other subdivisions of the angle section.
The above and other objects, features and advantages of the present invention will become apparent from the following particular description, taken in conjunction with the accompanying drawings which show by way of example some preferred embodiments of the present invention.